The disclosure relates to microfluidic devices and methods of manufacture and inspection thereof.
Microfluidic circuits are typically manufactured as planar structures from two substrates which are bonded together and arranged in a carrier. The carrier is sometimes referred to as a caddy. In the case of polymer substrates, solvent vapour bonding can be used to bond the substrates. For glass substrates, suitable cement can be used. Microfluidic circuit elements, such as channels and mixing chambers, are formed at the interface between the substrates by surface structure in one or both of the substrates. In addition, to supply fluid to the circuit and to remove fluid from the circuit, one of the substrates has through holes to provide external access, these through holes being aligned with corresponding through holes in the carrier. Fluid-tight seals are needed around these external access points to prevent liquid leakage or pressure loss between the carrier and the adjacent substrate. These seals are conventionally provided by O-rings or other forms of gasket made of resilient material.
FIG. 8 is a schematic cross-section showing features of such a conventional microfluidic device. The device comprises first and second substrates 2 and 4 arranged in a carrier 6. A laterally extending channel 12 is shown at the interface between the substrates formed by surface structure on one face of the first substrate 2. The second substrate 4 has a through hole 10 which is in fluid communication with the channel 12 and which is aligned with a further through hole 8 in the carrier. An O-ring 27 is arranged around the through hole 8/10 (as considered in plan view) at the interface between the second substrate 4 and the carrier 6. Location of the O-ring 27 is aided by ring-shaped grooves or surface indentations 28 in the carrier 6 and/or second substrate 4 (both in the figure). One end of a male luer connector 26 is also schematically illustrated having a tip portion with a diameter dimensioned to fit into the hole 10 and a location portion having a larger diameter which is greater than the diameter of the hole 10, but less than the diameter of the hole 8, so that a shoulder is formed at the transition between the location portion and tip portion which serves as an abutment surface. The holes 8 and 10 and seal 27, 28 therefore collectively form a female luer connection.
FIG. 9 is a schematic cross-section showing features of a specific prior art device from US 2011/0243813 A1. An opaque layer 4 is sandwiched between transparent layers 2, 6. The layer 4 is perforated to carry a microfluidic circuit structure made up of channels, mixing chambers and so forth, whereas the layers 2 and 6 are essentially unstructured except for layer 6 carrying an inlet port and a vent for external fluid communication. Specifically, layer 6 has a through hole 8 for external input of liquid, which is in fluid communication with a larger diameter chamber 15 formed in layer 4 which leads into a capillary channel 12, also formed in layer 4. Laser welding is used to bond the layers together.
US 2004/0148777 A1 also discloses a microfluidic device made of two, three or four rigid layers in which laser welding is used to bond the layers together.
FIG. 10 is a schematic cross-section showing features of a specific prior art device from WO 2011/113630 A2. First and second substrate layers 2 and 6 sandwich a resilient elastomeric gasket layer 4 which is also opaque to laser radiation from a laser welding apparatus. A channel 12 is formed by mutually facing surface structure in the substrate layers 2 and 6, and a similarly shaped aperture in the gasket layer 4. The channel 12 is sealed by a laser weld 20 having a weld seam or weld joint which partly or fully runs around the channel 12 and which is somewhat laterally offset from the channel 12.
US 2011/0076204 A1 discloses a valve for a microfluidic device which employs a three layer structure similar to FIG. 10 with two outer layers sandwiching an elastomeric middle layer. Again similar to the device of FIG. 10, a seam weld is provided by laser welding in a joint line around the channel somewhat laterally offset from the channel 12.